ok...as there are different people on different forums. Except I started a thread here to get answers...when u ask a question like this in a thread about something else it usually get passed over. But thanks for the useless comment

it really depends on your engine , firing timing , compression ratio ...
about your car, difference isn't that big so you can't see any difference on dyno (like 2 hp) but you can feel the engine is different with higher octane.
if it's an old car with lower compression ratio , high octane probably hurt the engine.

It can not sound like anything when it's not said. Yea I guess the latter part is a streatch but we should all try to not always think everyone is after each other and read things differently. All I said was same question different forum to me what that means is same question different answers we only get opinions!

also considering throwing in some 100 octane and trying some 60-130 runs. Would be interesting to see what happens.

The ECU is able to adapt for a couple of points of higher (or lower) octane. I believe it can advance timing enough for 95 octane or so (this is just approximate figure given to us from multiple tuners over the years).

On a stock car, using 93 octane is not much different than using 91 octane. There is a slight difference in performance but not much. However, using 100 octane (unleaded of course) would give you a noticeable difference over 91 octane, but it is still not a BIG difference.

On a car that is tuned for 91 or 93 octane, using 100 octane gas yields the same amount of difference that you would see by using 100 octane on a stock car as the ECU would adapt slightly.

On a car that is tuned for 100+ octane level, using 100 octane gas would give you a significant increase in power. On an E55, I've seen a gain of +38 rwhp and on a C63, I've seen +27 whp.

my friend who just got a 5.0 stang got tuned at steeda. the car comes stock with a 91 octane tune. steeda's 93 octane tune was a 'big improvement' he said, that it was 'more power all over the band' good stuff. then he got a ram air intake, and tuned for it, and then said that it felt like the same increase in power, more or less, but opened up the top end, he felt like it breathed better (common comment). now this is one specific car, changing octane on a FI car is another ball game imho, more octane = more resistance to knock.

The ECU is able to adapt for a couple of points of higher (or lower) octane. I believe it can advance timing enough for 95 octane or so (this is just approximate figure given to us from multiple tuners over the years).

On a stock car, using 93 octane is not much different than using 91 octane. There is a slight difference in performance but not much. However, using 100 octane (unleaded of course) would give you a noticeable difference over 91 octane, but it is still not a BIG difference.

On a car that is tuned for 91 or 93 octane, using 100 octane gas yields the same amount of difference that you would see by using 100 octane on a stock car as the ECU would adapt slightly.

On a car that is tuned for 100+ octane level, using 100 octane gas would give you a significant increase in power. On an E55, I've seen a gain of +38 rwhp and on a C63, I've seen +27 whp.

We can only get 91 octane here in NB Can. I looked at raising octane by adding octane boost (very expensive), race gas (less expensive and hard to locate locally) or toluene (expensive). I gave up because the cost/value relationship seemed too extreme on the cost side for questionable benefits on the value side. I guess if you can't get the big companies to mix it it is not worth it especially for a daily driver. Occasionally at the track is a different matter because you are WOT all the time and max performance is what you are after so it makes it more worthwhile.

We can only get 91 octane here in NB Can. I looked at raising octane by adding octane boost (very expensive), race gas (less expensive and hard to locate locally) or toluene (expensive). I gave up because the cost/value relationship seemed too extreme on the cost side for questionable benefits on the value side. I guess if you can't get the big companies to mix it it is not worth it especially for a daily driver. Occasionally at the track is a different matter because you are WOT all the time and max performance is what you are after so it makes it more worthwhile.

honestly on the M156 motors, 91 octane and 93 octane in stock form will not make much of a power difference, the vehicle may run slightly better as the ME will not have to pull back but the numbers themselves would maybe vary 1-3hp which could be contributed to many things such as a weather. however the difference in 2 points of octane will become more and more important the further you go in modifications.... we have currently built a P800 Switzer 996tt, and the difference in octane from the east (93octane) and the west (91 octane) equals a difference in 2PSI of boost... on the dyno on this particular vehicle equals 50whp.... but we are talking about pushing the envelop safely, in a stock or tuned only M156 ECU the differences in my opinion, is slight. Stock being 1-5hp, tuned being 3-10hp, as you can see the more modifications the larger the difference in power becomes.

honestly on the M156 motors, 91 octane and 93 octane in stock form will not make much of a power difference, the vehicle may run slightly better as the ME will not have to pull back but the numbers themselves would maybe vary 1-3hp which could be contributed to many things such as a weather. however the difference in 2 points of octane will become more and more important the further you go in modifications.... we have currently built a P800 Switzer 996tt, and the difference in octane from the east (93octane) and the west (91 octane) equals a difference in 2PSI of boost... on the dyno on this particular vehicle equals 50whp.... but we are talking about pushing the envelop safely, in a stock or tuned only M156 ECU the differences in my opinion, is slight. Stock being 1-5hp, tuned being 3-10hp, as you can see the more modifications the larger the difference in power becomes.

If your ECU is written for 100 octane you will not receive the full potential of the 100 octane fuel. the car will adapt up to roughly 95 octane on its own providing you with a nice increase of power over the 91 octane ~10-20hp, but will not give you full 25-35hp that you could receive.